The present invention relates to a method and apparatus for recirculating exhaust gases in a diesel engine so as to suppress the emission of especially nitrogen oxides (NOx).
In order to suppress the emission of nitrogen oxides from internal combustion engines of automobiles, there have been widely used a variety of exhaust gas recirculation apparatus in which part of the exhaust gases is recirculated into an intake system. In the case of diesel engines, an exhaust gas recirculation ratio, that is, the ratio of the quantity of exhaust gases to be recirculated to the quantity of intake air plus the quantity of exhaust gases to be recirculated, is in general decreased with the increase in the load on the engine. In practice, with the prior art exhaust gas recirculation apparatus for the diesel engines, the exhaust gas recirculation ratio has been controlled in response to pushing down of the accelerator pedal.
With such prior art apparatus, the exhaust gas recirculation ratio is controlled in response to variations in load on the engine with the load corresponding to the amount of depression of an accelerator pedal in the case where the pedal is to be operated in response to variations, in the load to maintain a running speed of the engine constant. When the accelerator pedal is maintained at a predetermined stroke, however, variations in the load may cause variations in the rotational speed of the engine, but not in the exhaust gas recirculation ratio. Thus the prior art exhaust gas recirculation apparatus cannot attain any control of the exhaust gas recirculation ratio in response to the load over the entire operating conditions of the engine while such control is performed in response to the load only under the limited operating conditions.
It is an object of the present invention to eliminate the disadvantages of the prior art apparatus by controlling an amount of recirculating exhaust gases in response to an amount of fuel injection based on the fact that an amount of fuel injection is closely related to a load on a diesel engine.